This invention relates to a radial flow fan with a central drive motor arranged coaxially with respect to a fan wheel or impeller and substantially inside this fan wheel, wherein the fan wheel diameter is larger than three times its axial length, with air inlet ports disposed at one large-area end face of a fan casing or housing, and with radial discharge through an exhaust port arranged in the casing adjacent the circumference of the fan wheel. Fans of this type serve for the ventilation and/or heat removal in photomechanical or electronic equipment or similar devices. The requirements to be met by such a fan, in addition to the maintenance of certain dimensions for installation in given apparatus, are an optimum conveying power (volume/time in dependence on the pressure) and low noise.
U.S. Pat. No. 3,597,117, which is incorporated herein by reference, discloses a fan of the above-mentioned type. Although the fan of this patent is of relatively small volumetric construction, it is disadvantageous with respect to complexity of construction, and delivery efficiency. The present invention is directed in part to overcoming these disadvantages.
The invention is based on the problem of improving the delivery efficiency of a radial flow fan of the above-described type. This objective is accomplished, according to one aspect of the invention, by providing the large-area end face of the casing which is disposed oppositely to the end face with the air inlet ports with a metallic plate which is connected with good heat conductance with the stator of the drive motor. (See plate 4, stator 1, rotor 2 in FIG. 3). This feature of the present invention makes it possible to place a greater load on the motor, without the latter reaching or exceeding a maximum, permissible critical temperature. Therefore a rotor with a higher moment requirement can be utilized and thus effectively a better delivery efficiency can be attained for a given total installation, size and energy input.
The present invention further contemplates providing the fan drive motor with an external rotor and internal stator and to mount the internal stator over its central coaxial bearing sleeve, with an end-face flange to the metallic plate 4, preferably in a releasable manner.
For an additional support of the intended effect, the present invention further contemplates providing additional heat-dissipating means arranged between the coil winding heads of the rotor and the metallic plate 4.
For a clearly economical realization of the present invention, it is furthermore proposed to fashion the motor as a double-pole shaded-pole motor with such a position in the housing or casing that a pole clearance, i.e. also a coil winding head gap of the stator, is oriented toward the exhaust port.
In an alternative preferred embodiment, a considerable improvement is also obtained by providing the drive motor with a symmetrical polyphase winding. This permits a reduction of the size of the motor and, correspondingly, affords a further improvement in the flow characteristic of the fan, for example due to the fact that the flow can be controlled more effectively since impeding fixed components have become smaller.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.